Method of manufacturing resistors



Patented May 2, 1933 UNITED STATES PATENT oF Ic JOSEPH A. FLANZER, OF BROOKLYNZ NEW YORK, ASSIIGNOR TO TECHNIDYNE COR- I PORATION, OF NEW YORK, N.Y.,

A CORPORATION OF NEW YORK METHOD OF IVLANUFACTURING RESISTORS No Drawing. Application filed April 15,

This invention relates to the manufac-. ture of electrical units and more particularly to the manufacture of resistors comprising an insulation base and a conductive or resistance paint coatedv thereon.

In the manufacture of electrical units such as resistors in which a conductive paint is coated on an insulation base, considerable difliculty arises in attempting to obtain uniform pre-determinable resistance values. After years of experience and continuous research in the development and use of numerous resistance paints, it became possible to bring the resistance value of units made in the same way, at any given time within tolerable limits, say a departure from a desired value of less than However,

the average value did not remain constant the base.

from day to day, and variations of as much as 200% would frequently occur. In fact even within the period of a single day, variations of 100% in resistance value have taken place. It was suggested that these variations might be due to changes in the composition of the paint, but control of the temperature of the paint supply, and limiting the permissible age of the same, did not greatly help in solving the problem.

The primary object of the present invention is to overcome the foregoing difliculty and to make it possible to obtain pre-determinable uniform resistance values when manufacturing painted resistance units. This I have found is possible by applying uniform drying methods when producing the units, for I have found that the resistance value of such a unit varies greatly with, and is approximately proportional 0 the time of drying of the paint on the ase.

I believe that this phenomenon may best be explained on the theory of chemical reaction taking place between the paint and For example, a preferred form of resistor employs a paint which contains colloidal graphite suspended in a vehicle of a metallic phosphate dissolved in dilute phosphoric acid with a slight excess of phosphoric acid over that necessary to dissolve the metallic phosphate, and the base reaction.

1930. Serial No. 444,614.

It is no solution of the difficulty to em-f ploy, for example, an acidproof enamel or, on the other hand, a non-acidic paint in order to prevent reaction therebetween, because the successful adhesion of the paint film to the glossy enamel surface seems to be dependent upon some reaction between the paint and the base.

In this aspect, the object of my invention is to cause a resistance film to adhere to an insulation base, and yet to obtain uniform resistance values 111 the film, and thls ob ject is fulfilled by coating the insulation.

base with a resistance paint whichchemically reacts with the base when wet but not when dry, and causing the paint to dry in a pre-determined time. More specifically an acid resistance paint is employedin conjunction with an ordinary white or basic enamel base.

A somewhat similar problem arises when painting a metallic paint on an insulation base as, for example, the silver paintused for terminals as disclosed inmy copending application Serial No. 411,736 filed Decemher 5, 1929. disclosed, Which, like the resistance paint mentioned above, includes a metallic phosphate and phosphoric acid, is painted directly on the enamel, high contact resistance lnayresult. The present invention, as already outlined, may be applied with equal utility to such a highly conductive paint as well as to the. relatively lowly conductive resistance paint first mentioned, or, in other words, it is generically applicable to con When the silver paint there- In some cases it is desirable to employ a.

plurality of superposed coats of resistance, paint in order to obtain a desired uniform, or nonuniform, resistance value in a resistance unit. In making such units, variations in resistance value may be extremely great because of variations in the resistance value of the first coat and unexpectedly augmented variations in the resistance value of successive layers applied to such a first coat. Slow drying of the first coat seems to result in a film which is mechanically weak and porus, as well as increased in resistance. A second layer of paint applied to such a. first coat is subject to reaction, probably because the second coat is permitted to come directly in contact with the enamel base, instead of being separated therefrom by a closely compacted first coat. Furthermore, slow dryingof the first paint film may result in neutralization of the acid content thereof, and even the formation of additional metallic salts which will result in the absorption of acid from sucdeeding coats of paint, whereby upsetting their chemical composition and, consequently, the resistance thereo -Another object of the present invention is to overcome these difficulties, and this may best be done by drying the first coat of resistance paint very rapidly, in which case the successive layers of paint are not affected by reaction with the insulation base. In fact, the protection afforded in this manner is so great that uniform drying of the additional coats of paint may, if desired, be dispensed with, though, of course, still more accurate results may be obtained by applying uniform drying methods to each of the coats of paint.

Still another and more specific object of my invention resides in the application of the foregoing principles to electrical units made with conductive paints, such as are disclosed in the applications of Lester L. Jones, Alois Schmidt, and Joseph Jones, Serial No. 167,583 filed February 11, 1927, now Patent 1,773,105, issued August 19, 1930, Lester L. Jones Serial No. 168,471 filed February 15, 1927, Joseph A. Flanzer, the present applicant, and Emil Reisman, Serial No. 393,573, Reisman, Serial No. 393,574, filed September 18, 1929, and the previously mentioned application of the present applicant, Serial No. 411,736 filed December 5, 1929, and applied to resistance units such as are disclosed in the following patents: 1,836,600, Dec. 15, 1931, and 1,819,246, August 18, 1931, to Lester L. Jones; and 1,808,790, June 9, 1931 to Emil Reisman.

To the accomplishment of the foregoing and such other objects as may hereinafter appear, my invention consists in the method steps, and their relation one to the other, as hereinafter are more particularly defiled September 18, 1929, Emil 0 scribed in the specification, and sought to be defined in the claims.

In the above identified copending applications, bothfixed and variable resistors phate dissolved in dilute phosphoric acid in a slight excess of phosphoric acid. In this vehicle various finely divided and preferably colloidal conducting media may be suspended, as, for example, graphite or carbon, or mixtures of the same with mica, or even metallic silver, depending, of course, upon the order of magnitude of resistance value desired. Such paints adhere tenaciously to many kinds ofinsulation base, and are particularly suitable for use on an enameled base; 3

While the individual units obtained by this method of manufacture were extremely satisfactory in operation, the method had the disadvantage, as a manufacturing proposition, that the resistance value obtained by using a particular formula of resistance paint could not be predetermined with any degree of accuracy. While it is possible to manufacture large numbers of the units and afterwards classify the same according to their measured resistance values, this is uneconomical and practically useless when it is necessary to fill quantity orders for resistors having values specified within close limits.

As has already been outlined, I have discovered that the desirable adhesion between the paint and the base is probably due to chemical reaction therebetween, and that thi s chemical. reaction alters the mechanical characteristics as well as the chemical composition, and ultimately, the resistance value of the film. I have further found that the reaction takes place when the paint is wet, but not when the paint is dry, and that therefore the extent of reaction may be controlled by regulating the drying time of the paint. A In a specific experiment, two units were similarly painted, and one was allowed to dry in about three minutes, while the drying of the other was prolonged to fifteen minutes. Both units were then similarly baked. The resistance value of the first unit was 200,000 ohms, while that of the second unit was 1,000,000 ohms. In general, experiment shows that the resistance value obtained is approximately proportional to the dr ing time. A variation in drying time 0 several minutes can readily cause a variation in resistance value of a 100% or more. Essentially, therefore, the present invention involves the application of unidry the units in the desired time.

form drying methods to the manufacture of electrical units inwhich a conductive paint is applied to an insulation base.

The drying time, of the paint depends upon the composition of the paint and the temperature and relative humidity of the surrounding atmosphere. In actually practicing my invention, two general methods may be followed, one of which involves relatii e humidity control, and the other of which does not. The first method is probably the best, but requires expensive plant equipment. In following this method, a room is provided in which the temperature and relative humidity are under continuous and accurate control. The units are painted in this room, and remain therein until dry. The temperature and relative liumidity in the room are selected in proper relation to the paint which is to be used, so as to In general, rapid drying is preferable to slow drying, and it is, therefore, recommended that the relative humidity be kept low, and the temperature comparatively high in the room, within limits of comfort to the workmen. The essential thing, of course, is that the relative humidity and the temperature be constant, because in such case uniform resistance values may be obtained,,and the desired resistance value may be obtained by selecting an appropriate formula of resistance paint.

My invention may also. be made use of in plants not equipped forrelative humidity control. In such case, the freshly painted units are preferably dried in a blast of warm,

or hot, air. This may be done'by using fir- 0f, the baking stage which it is customary drying box of any suitable known type/g many of which are provided with a moving conveyor, at one end of which the fresh ly painted units may be placed, and at the other end of which the dried units are received. The speed of the conveyor may be regulated to keep the units in the drying box, through which a current of warm air may be blown in opposite direction, for a specified time, say one minute.

When using this method, allowance must he made for the relative humidity of the air, if accurate results are to be obtained.

One way to do this is to increase the tem-- perature in the drying box when the relative humidity is high. The properv relationship between the relative humidity and the drying temperature is best determined empirically, because temperature affects the units in at least two ways: first, in altering the relative humidity of the air, and second, in affecting the drying time directly, and possibly, in other ways.

I Another way to compensate for variations in relative humidity is by varying the compositionof the paint used, according to the relative humidity at the time inquestion.

In this method, the temperature of the drying box is kept constant, and a series of paints are calibrated to obtain desired resistance values for different values of relative humidity, all at the specified constant temperature. The drying time employed may vary somewhat widely, so long as it is kept constant, for any particular line of resistance units made with a specified resistance paint, butvery slow drying is undesirable because the resulting paint film becomes mechanically weak and porous, and this is undesirable evenwhen a single coat of paint is used, and is particularly undesirable when succeeding coats are to be applied. Drying times ranging between one-half minute and three minutes have been employed with excellent results. This time may be considerably .increased, with a concomitant increase in resistance value, and without bad chemical effect, but if increased up to, say fifteen minutes, the resulting units are not satisfactory. Rapid drying, on the other hand, seems to be desirable, and ordinary commercial drying apparatus has proven incapable of drying units too rapidly, i. e. so rapidly as to totally prevent the desired initial chemical reaction. That is to say, I have been unable to dry the units, after they have been painted, so rapidly as to prevent that desirable initial chemical reaction which seems to result in the effective adhesion of the paint to the enamel.

It should be understood that the drying stage, which has been so far described, does not, in any way, eliminate, or take the place thereto for more detailed information on the subject. Ordinarily the resistance paint would be allowed to dry between the painting and the baking stages because the baking furnace is a large unit quite removed from the room in which the painting is performed. It, on the other hand, a plant is so laid out that the freshly painted units may be immediately led into the baking furnace, the latter may, itself, provide the desired rapid drying as well as baking of the units. Such an arrangement would not result in precisely uniform drying times but would result in rapid drying which greatly minimizes the changes in drying time and the consequent changes in resistance value.

A separate controlled drying step first recommended in the present disclosure is inries of paints which differ from each otherretardation and inhibition of a chemical reaction between the paint and the base by controlling the drying time of the paint instead of permitting this time to vary haphazardly in accordance with current weather conditions. If the particular paint in question is such that it is desirable additionally to bake the unit, then the baking may be proceeded with" at any convenient subsequent time. On the other hand, if the conductive paint is such that baking is not essential, the baking step need, of course, not be added. I v

By the practice .of my invention, it has been determined that the resistance paints are themselves perfectly stable, and that it is commercially practicable to provide a sein specific resistance in small and carefully calibrated steps, say 10% apart. Upon re- 1 ceiving an order for a quantity of resistance 'I clude all these methods in the units of specified resistance value, the proper paint, or combination of paints when successive coats are to be used, may be selected, and the resistance value of the resulting units may be predicted with certainty. When making units provided with multiple coats of paint I especially recommend that the first coat be rapidly dried, for insuch case little variation may be anticipated in the resistance value of a succeeding coat. However, for best results, it is clear that uniform drying methods may be applied to each "of the several coats of paint.

The method of practicing my'i'nvention, and the many advantages thereof, will be apparent from the foregoing description. Precision in the resistance value of units made'at the same time is increased, and 1mprovement in the relative precision of the average resistance value over a period of days, or in the event of changes in weather, is very extraordinary. Resistance values may be predicted in advance, and various formulae of resistance paint may be closely calibrated so as to make it readily possible to meet specifications. The mechanical characteristics of the paint film are improved and pre-determinable.

The control of the drying time depends upon the paint composition, the temperature and the relative humidity of the surrounding atmosphere,.and it has previously been explained that either temperature or paint composition may be controlled, to compensate for changes in relative humidity when direct control of relative humidity is inconvenient on impossible. I intend to inappended is regulated by properly relating the. paint composition and the temperature and relative humidity bf the surrounding atmosphere.

It will apparent that while I have shown and. described my invention in the preferred forms, many changes and modifications may be made in the methods disclosed without departing from the spirit of the invention, defined in the following claims. Particularly, the invention may be considered as either the use of uniform drying time or rapid drying time, or uniform rapid drying time, all of which will be generically referred to as controlled or regulated drying time.

\Vhat I claim is: j

1. In the manufacture of electrical units comprising an insulation base and a conductive paint which reacts with the base when wet, the method of controlling the extent of reaction which includes the step of regulating the drying time of the paint.

2. In the manufacture of electrical units comprising an insulation base and a conductive paint which reacts with the base when wet, the methodof controlling the extent of reaction which includes the step of regulating the drying time of the paint by properly relating the paint composition and the temperature and relative humidity of the comprising an ordinary basic enamel base and a conductive paint including an acid, the method of controlling the extent of reaction between the paint and the base which includes the step of regulating the drying time of the paint by properly rel ting the paint composition and the temper...ure and relative humidity of the surrounding atmosphere.

5. In the manufacture of resistance units comprising an ordinary white enamel base and a resistance paint comprising colloidal graphite, metallic phosphate, and phosphoric acid, the method which includes controlling the extent of reaction between the paint and the base by regulating the drying time of the paint.

6. In the manufacture of resistance units comprising an ordinary basic enamel base and a resistance paint comprising colloidal graphite, metallic phosphate, and phosphoric acid, the method of controlling the extent of reaction between the paint and'the base which includes the step of regulating the drying time of the paint by properly relating the paint composition and the temperature and relative humidity of the surrounding atmosphere.

7. In the manufacture of resistance units comprising a' resistance film coated on a base,

the method of causing the film to adhere to the base and of obtaining uniform resistance values which includes coating an insulation base with a resistance paint which chemically reacts with the base when wet but not when dry, and causing the paint to dry in a pre-determined time.

8. In the manufacture of resistance units comprising a resistance film coated on a basic enamel base, the method of causing the film to adhere to the base and of obtaining uniform resistance values which includes coating the base with an acid resistance paint which chemically reacts with the enamel when wet but not when dry, and causing the paint to dry in a pro-determined time.

9. In the manufacture of resistance units comprising a resistance film coated on a base, the method of causing the film to adhere to the base and ".of obtaining uniform resist-- ance values which includes coating an insulation base with a resistance paint which chemically reacts with the base when wet but not when dry, and drying the paint very rapidly in order to limit the extent of reaction.

10. In the manufacture of resistance units comprising a resistance film coated on a basic enamel base, the method of causing the film to adhere to the base and of obtaining uniform resistance values which includes coating thebase with an acid resistance, paint which chemically reacts with the enamel when wet but not when dry, and drying the paint very rapidly in order to limit the extent of reaction.

11. In. the manufacture of resistance units comprising an insulation base and a plu rality of coats of resistance paint which when wet react with the base, the method which includes painting the base with the first coat of paint, drying the paint in a predetermined time, and thereafter painting the first coat of paint with one or more further coats of paint. y

12. In the manufacture of resistance units comprising an insulation base and a plurality of coats of resistance paint which when wet react with the base, the method which includes painting the base with the first coat of paint, drying the paint in a pro-determined time, painting the first coat of paint with one or more furthercoats of paint, and controlling the drying time of each of said further coats of paint.

13. In the manufacture of resistance units comprising an insulation base and a plu- "rality of coats of resistance paint which when wet react with the base, the method which includes painting the base with the first c'oat'of paint, drying the paint very rapidly, and thereafter painting the first coat of paint with one or more further coats of paint.

.14. In the'ma'nufacture of resistance units comprising an insulation base and a plurality of coats of resistance paint which when wet react with the base, the method which includes painting the base with the first coat of paint, drying the paint very rapidly, painting the first coat of paint with one or'more further coats of paint, and controlling the. drying time of each of said further coats of paint.

15. In the manufacture of resistance units comprising a basic enamel insulation base and a plurality of coats of acid resistance paint which when wet reacts with the enamel, the method which includes painting the base with the first coat of paint, drying the paint very rapidly, and thereafter painting the first coat of paint with one or more further coats of paint.

16. In the manufacture of resistance units comprising a basic enamel insulation base and a plurality of coats of acid resistance paint which when wet reacts with the enamel, the method which includes painting the base with the first coat of paint,

drying the paint very rapidly, painting the of New York and State of New York this 10th day of April A. D. 1930.

JOSEPH A. FLAI ZER. 

